1. Field of the Invention
This invention relates to a solar-cell module comprising a photovoltaic device sealed on a reinforcing sheet with a filler material, a process for its production, a building material making use of it, a method for laying the building material, and an electricity generation system.
2. Related Background Art
Solar-cell modules employing reinforcing sheets on their back sides are known in the art. As an example thereof, a general-purpose solar-cell module having an aluminum frame material as shown in FIG. 8 will be briefly described below.
FIG. 8 is a perspective view showing a conventional solar-cell module. Reference numeral 1 denotes a solar-cell module; 2, a photovoltaic device; and 7, a frame. FIG. 9 is an enlarged cross-sectional view along the cross section 9--9 in FIG. 8.
How the solar-cell module 1 of this example is made up will be described with reference to FIG. 9. The solar-cell module 1 of the present example comprises a photovoltaic device 2 resin-sealed with a light-transmissive resin 3. The light-transmissive resin 3 functions as a filler material for sealing the photovoltaic device and also fixing the device onto a reinforcing sheet. In this example, the solar-cell module 1 has a light-transmissive surface protective film 4 on the outermost surface on its light-receiving side and has a metallic reinforcing sheet as a reinforcing sheet 105. These are bonded through the light-transmissive resin 3 into a laminate.
The solar-cell module 1 is provided with an aluminum frame 7 on its side portion. Using this aluminum frame, the solar-cell module 1 can be fixed to any desired place. From the solar-cell module 1 of the present example, its electricity is outputted through a cable 10 led out of a terminal lead-out box 8 fixed to the reinforcing sheet 5 with an adhesive 9.
An example of how to make a solar-cell module by sealing-and-fixing will be briefly described below. First, as constituent materials used to produce the solar-cell module by sealing and fixing the photovoltaic device, the following ones are prepared.
For example, an EVA resin (ethylene-vinyl acetate copolymer) is formed into a sheet of 450 .mu.m thick as a filler material which covers the surface and back of the photovoltaic device and also has the function to bond other constituent materials provided on its outer surfaces, and two sheets are prepared for the top and the back. Also, for example, a fluorine resin film of 50 .mu.m thick is prepared as a surface protective film. Still also, for example, a galvanized steel sheet of 0.4 mm thick is prepared as a reinforcing sheet provided on the back of the solar-cell module.
Here, as the photovoltaic device, a photovoltaic device formed of, e.g., amorphous silicon is prepared. This is a photovoltaic device comprising a stainless steel substrate of 125 .mu.m thick and formed thereon an amorphous silicon semiconductor layer.
The constituent materials thus prepared are sealed and fixed by contact bonding with heating. FIG. 10 is a perspective view showing an example of a sealing-and-fixing jig. FIG. 11 is a cross section corresponding to the part along the line 11--11 in FIG. 10, which shows a course of procedure during which materials for producing a solar-cell module are placed on the jig. The jig, 18, is made up using a plate made of aluminum, and is so used that the photovoltaic device and the material that constitutes the filler material are placed thereon. In the plate made of aluminum, in order for it to function as the jig, a groove 19 is provided along its outer sides in such a way that the groove surrounds the region where the photovoltaic device and the filler material are placed, and an O-ring 20 made of a heat-resistant resin is fitted in the groove. Right on the inner side of the O-ring 20, suction holes 21 for making a vacuum are provided, which are connected to a pipe 22, and the pipe 22 is further connected to a vacuum pump (not shown). The pipe 22 is also provided with a valve 26.
By the use of such a jig, the solar-cell module is produced, e.g., in the following way. First, a Teflon film for release 23 is spread on the surface of the jig. This is done in order to prevent the filler material EVA resin from being pressed out to adhere to the jig 18. Next, the materials prepared as described above are superposed on the jig. More specifically, as the reinforcing sheet, the galvanized steel sheet of 0.4 mm thick is placed at the lowest position, and on this sheet the EVA resin formed into a sheet of 450 .mu.m thick as the filler material, the amorphous silicon photovoltaic device, the like EVA resin and the uppermost, fluorine resin film of 50 .mu.m thick are successively superposed to form a laminate 24, which is then placed on the release Teflon film 23. Here, as the fluorine resin film, a sheet having a larger size than that of the EVA resin sheet is used. Thus, like the spreading of the release Teflon film on the bottom, the filler material can be prevented from being pressed out to adhere to other materials members. A silicone rubber 25 is finally placed on the laminate thus prepared, thus the materials are completely superposed on the jig 18.
Under this condition, the vacuum pump (not shown) is actuated to make the valve 26 open, so that the silicone rubber 25 is brought into close contact with the O-ring 20 and hence a closed space is formed which is defined by the silicone rubber 25, the O-ring 20 and the aluminum plate of the jig 18. The inside of the space stands vacuum. Thus, the reinforcing sheet, the filler material, the photovoltaic device, the filler material and the light-transmissive surface protective film are uniformly pressed against the jig 18 under atmospheric pressure through the silicone rubber 25.
The jig 18 standing as stated above is put into a heating oven while keeping the vacuum pump operating, i.e., while maintaining the vacuum condition. The temperature in the heating oven is maintained at a temperature higher than the melting point of the filler material. After the filler material has been heated to the temperature higher than its melting point to become soft and the time for which it completes a chemical change for exhibiting a sufficient adhesive force has lapsed, the jig kept standing vacuum is taken out of the heating oven. This is cooled to room temperature, and thereafter the vacuum pump is stopped operating, and the silicone rubber 25 is removed so as to be released from the vacuum condition. Thus, the solar-cell module can be obtained.
The solar-cell module is produced in this way. There, however, is a problem that, when the above materials are superposed and thereafter put into a vacuum, the air present between the reinforcing sheet, galvanized steel sheet and the filler material EVA resin can not be completely sucked up with the vacuum pump.
More specifically, as shown in FIG. 12, the filler material, EVA resin (light-transmissive resin) 3 and the reinforcing sheet, galvanized steel sheet 105 may undesirably be brought into close contact in such a state that they have trapped air 27 at some part between them. In FIG. 12, reference numeral 4 denotes the protective film. This may frequently occur when, e.g., the filler material EVA resin absorbs moisture and the reinforcing sheet has a very flat surface. Once they have been brought into such a state, the air 27 at that part can not be sucked up however it is tried being sucked with the vacuum pump, and it follows that the solar-cell module is produced by sealing-and-fixing as it is. As the result, there occur trapped air portions where the EVA resin and the reinforcing sheet are not in close contact.
Meanwhile, there is an increasing commercial demand for large-area solar-cell modules. The above problem may become more serious when large-sized, large-area solar-cell modules are manufactured. As solar-cell modules come to have a larger size and larger area, the distance from the middle to the end of a solar-cell module becomes larger, resulting in a great increase in resistance when the air is removed. This problem has occurred even in solar-cell modules having caused no problem of the occurrence of trapped air portions, when they are simply made larger in size so as to meet the commercial demand.
The trapped air portions may result in great damage of appearance if they are large, so that products obtained can not be brought into the market. This can be the cause of a decrease in yield of manufacture, consequently bringing about a problem of an increase in production cost.
As for an instance where the trapped air portions are small and also they are present on the back of the photovoltaic device, there is a problem that they can not be found by visual inspection before the shipment of products. What is meant by the fact that they are not found by visual inspection is that there is no problem on appearance in the initial state. However, during the long-term use of solar-cell modules, the air in such small trapped air portions repeatedly increase and decrease in volume, and hence they may grow into larger trapped air portions. This may cause a problem on appearance. Also, in the course of such growth, the trapped air portions may internally cause a phenomenon of sweating or moisture condensation to gather water content. In such an instance, the water content may permeate into the photovoltaic device to cause a problem of lowering electrical performance of the photovoltaic device in some cases.